Development of receivers for Satellite Positioning Systems (SATPSs), such as Global Positioning System (GPS) receivers, with inaccuracies as small as a few centimeters has opened many survey and navigation activities to collection of position data using SATPS technology. High accuracy mapping using SATPS can be performed in real time, or the data can be post-processed.
An SATPS usually includes, at the minimum; an SATPS antenna that receives SATPS signals from a plurality (preferably four or more) SATPS satellites; an SATPS receiver/processor that receives and processes these signals from the antenna to estimate the present time and/or location of the system; and an information storage or output means to store this information, to display this information, or to deliver this time/location information to another entity for its subsequent use. The system location of the SATPS is usually the antenna location. An object to be mapped in a survey may not permit the the SATPS antenna to be positioned contiguous to or on top of the object. Examples of such objects include utility poles, buildings, signs, trees, motorized equipment, animal homes and habitats, and communications and radio tower structures. Where an SATPS has associated location inaccuracies of no more than a few centimeters, it is pointless to position the SATPS antenna several meters from the object to be mapped.
Some workers in this field have developed portable or semi-portable equipment that can be used to assist surveying of a given land parcel, although this equipment often requires line-of-sight measurements that are inconsistent with mapping of opaque or partly opaque structures such as buildings and towers.
A geodetic survey system using a digital phase meter is disclosed by Jaffe in U.S. Pat. No. 3,522,992. The apparatus measures distances and changes therein between a transmitter and a receiver, by combining, modulating and transmitting two laser beams having different frequencies and measuring their corresponding phase difference at the receiver. The modulated composite light beam is split by a dichroic mirror, and the phase and intensity of each of the two frequency component signals (modulated) is analyzed to determine an initial or reference modulated waveform. The reference waveform is compared with a subsequently received waveform having the same signal frequency to determine any changes in the transmitter-to-receiver optical distance or in the refractive index of the intervening transmission medium. This apparatus requires transmission of two or more light beams along a line of sight, and the apparatus does not appear to be portable.
In U.S. Pat. No. 3,619,499, Petrocelli discloses a surveying system that measures small displacements of a light source. The light source is attached to a movable body and is monitored by a television camera. The video image is approximately centered on an image screen, and most or all other ambient light is filtered out from the screen image. The number of raster sweeps from the edge of the screen to the edge of the light source image is counted so that a small or large movement of the light source is monitored as a corresponding displacement of the light source image on the screen.
A guidance system for an earth-working vehicle, such as a tractor, is disclosed in U.S. Pat. No. 4,244,123, issued to Lazure et al. A signal transmitter, such as a rotating laser beam source, is positioned in a field to be worked, and two signal receivers are positioned at fixed, spaced apart, longitudinal locations on the vehicle, to distinguish changes by the vehicle in two horizontal directions. The receivers determine and report on the present location and bearing of the vehicle, based on what may be a phase difference of the signals received at the two receivers.
U.S. Pat. No. 4,309,758, issued to Halsall et al, discloses an unmanned land vehicle guided by three omni-directional light detectors carried on the vehicle. At least two spaced apart light sources must be provided off the vehicle, with each detector receiving light from two of the light sources. The vehicle bearing and location appear to be determined by signal phase differences for light from a common source arriving at the different detectors.
Gates et al, in U.S. Pat. Nos. 4,396,942 and U.S. Pat. No. 5,073,819, disclose method and apparatus for a video survey conducted by a television camera mounted on a top surface of a truck or other vehicle that moves along a road to be surveyed. The displated video image includes an electronically activated overlay image that provides a geometric baselines and allows actual distances to be estimated and/or video-recorded, using perspective views of the road as the truck moves along.
A guidance and control system for one or more land vehicles is disclosed in U.S. Pat. No. 4,647,784, issued to Stephens. Each vehicle generates and transmits a light beam that is reflected from each of two or more reflectors, each reflector having its own optical code (for example, stripes having different light reflectivities) and being oriented to reflect and return the light beam to a light detector carried by the vehicle. The returned light beams from each beam are analyzed to determine the present bearing of the vehicle.
U.S. Pat. No. 4,671,654, issued to Miyahara et al, discloses automatic surveying apparatus for surveying a route, to be used for a tunnel with curves therein. A laser beam is received at, and produces a light spot on, one or two projection screens. The light spot coordinates on a screen are determined by a screen image pick-up. Position and angular deviations from a desired route, of a moving target containing the laser light source, can be monitored and measured as the target moves along or adjacent to the desired route.
As disclosed by Goyet in U.S. Pat. No. 4,677,555, a rotating laser beam defines a reference plane for an earthworking vehicle, such as a pipelaying machine. Datum points, defined by several beacons fixed in the ground and indicating the pattern (bearing, elevation) to be followed by the vehicle, are provided. A microcomputer carried on the vehicle monitors the pattern actually followed by the vehicle.
Kamel et al, in U.S. Pat. Nos. 4,688,092 and U.S. Pat. No. 4,746,976, disclose a method for satellite navigation, using image pixels with precisely known corresponding latitude and longitude coordinates of a portion of a celestial body such as the Earth. A computer receives these images and generates a model of the satellite orbit, longitude, latitude and altitude as a function of time, with reference to the celestial body. A least squares algorithm converts the measurements into best-fit coordinates.
A method of automatically steering a land vehicle, such as a tractor, along a selected course in a field is disclosed in U.S. Pat. No. 4,700,301, issued to Dyke. A rotating laser beam source and directional light detector/processor are mounted on the vehicle, and two or more reflectors are positioned at or near the boundary of the field. The laser beam is reflected from the reflectors, returns toward the vehicle, and is received by the detector/processor, which determines the present location of the vehicle and its present bearing. In another alternative, two rotating laser beam sources are positioned near the edge of the field, the the laser beams emitted by these sources are received by an omni-directional light detector carried on the vehicle.
Use of a rotating laser beam for two-dimensional navigation of a land vehicle in a specified region is also disclosed by Boultinghouse et al in U.S. Pat. No. 4,796,198. Three or more reflectors, one having a distinctive reflectivity, are positioned near the boundary of the region reflect the laser beam back to the vehicle, where the reflected beams are received by a photoelectric cell and generate signals with associated beam arrival directions that allow determination of the present location of the vehicle. Distinctive reflection from the one mirror provides an indication of the angular position of the laser beam on each rotation.
U.S. Pat. No. 4,807,131, issued to Clegg, discloses an automated land grading system in which the position of a cutting blade is controlled automatically to provide controlled shaping of a land region being graded. A laser beam is projected in a predetermined pattern across the land region, and a laser detector carried on the grading machine receives the beam and approximately determines the location of the cutting blade and the blade angle and depth appropriate for grading that location in the land region. Information on the desired blade angle and depth is stored a microprocessor carried on the grading machine and is compared with the actual blade angle and depth to correct the blade orientation and elevation.
Olsen et al disclose survey apparatus for collection and processing of geophysical signals, using a Global Positioning System (GPS), a GPS base station and one or more data acquisition vehicles, in U.S. Pat. No. 4,814,711. Each vehicle carries geophysical measuring instruments, a GPS signal receiver and processor to determine present location, a visual display of present location, and radio communication equipment to transmit location information to the base station. The base station periodically polls and determines the present location of each vehicle, with reference to a selected survey course that a vehicle is to follow. The base station transmits commands to each vehicle to keep that vehicle on the selected course. Each vehicle also transmits results of the geophysical data it has measured to the base station for correlation and possible display at the base station. This apparatus requires continual tracking, control and correction of the course of each vehicle relative to the desired course and requires use of non-portable apparatus (a vehicle and its equipment) to provide the desired location and data measurements. All such measurements are transmitted to, and analyzed by, the stationary base station, and the measurements probably are accurate only to within a few meters.
U.S. Pat. Nos. 4,870,422 and U.S. Pat. No. 5,014,066, issued to Counselman, disclose method and apparatus for measuring the length of a baseline vector between two survey marks on the Earth's surface, using a GPS signal antenna, receiver and processor located at each mark to determine the location of at mark (accurate to within a few meters). The location data are determined using GPS carrier phase measurements at each survey mark and are transmitted to a base station for analysis to determine the baseline vector length between the two marks. This approach requires use of two spaced apart survey marks and a base station. Use of GPS signals from five or more GPS satellites and use of a surveying time interval of length .DELTA.t.gtoreq.5000 seconds are required in order to reduce the mark location inaccuracies to a less than a centimeter.
Paramythioti et al, in U.S. Pat. No. 4,873,449, disclose method and apparatus for three-dimensional surveying, using triangulation and a laser beam that propagates along the perimeter of a triangle. A rotatable mirror, a component of the scene to be surveyed, and a light-sensing means are located at the three vertices of the triangle, and knowledge of the angles of orientation of the rotatable mirror and the camera allow determination of the location of the component of the scene presently being surveyed. Three fixed, spaced apart stations, including one station at the scene to be surveyed, and receipt of a line-of-sight light beam are required here.
Apparatus for determining compass headings, using two GPS antennas located at fixed positions aboard a ship or aircraft, is disclosed in U.S. Pat. No. 4,881,080, issued to Jablonski. The absolute positions of the GPS antennas, with the usual inaccuracies, are measured without use of differential GPS. A GPS receiver/processor receives the signals sensed by the GPS antennas and determines a compass heading of the ship or aircraft, based upon the known relative positions of the two antennas on the ship or aircraft. A similar configuration, applied to mapping of ocean currents from an aircraft, is disclosed by Young in U.S. Pat. No. 4,990,922.
Use of three or more GPS antennas, arranged in a collinear or non-collinear array on a body, to determine the attitude or angular position of the body, is disclosed by Hwang in U.S. Pat. No. 5,021,792 and by Timothy in U.S. Pat. No. 5,101,356.
Gaer, in U.S. Pat. No. 4,924,448, discloses survey apparatus and method for mapping a portion of an ocean bottom. Two ships, each equipped with identical GPS signal antennas, receivers and processors, move along two parallel routes a fixed distance apart on the surface of an ocean. Each ship takes radio soundings of a small region of the ocean bottom directly beneath itself and receives a reflected radio sound from that same region that is originally transmitted by the other ship. The depths of the region directly beneath each ship, as determined by each of the two radio sound waveforms and by the GPS-determined locations of the two ships, are determined and compared for purposes of calibration.
A portable target indicator system, for use in a battlefield, is disclosed by Ruszkowski in U.S. Pat. No. 4,949,089. The target locator system includes GPS antenna and receiver/processor, a radio transmitter, a laser rangefinder and azimuth angle indicator. A rifleman carries the system into the battlefield and directs the laser rangefinder at a target. The radio transmitter transmits the rifleman's GPD-determined location and the offset location of the target relative to the rifleman to another entity, such as an aircraft, that has a weapons delivery system to be used against the target.
In U.S. Pat. No. 4,954,833, issued to Evans et al, a method for determining the location of a selected and fixed target or site, using a combination of GPS signals and the local direction of gravitational force. Geodetic azimuth is determined using GPS signals, and the local gravitational force vector is used to relate this location to an astronomy azimuth, using a fixed coordinate system that is independent of the local coordinate system. The target and a reference site are each provided with a GPS signal antenna, receiver and processor to determine the local geodetic azimuth.
Evans, in U.S. Pat. No. 5,030,957, discloses a method for simultaneously measuring orthometric and geometric heights of a site on the Earth's surface. Two or more leveling rods held at fixed, spaced apart locations, with a known baseline vector between the rods. Each rod holds a GPS signal antenna, receiver and processor that determines a GPS location for each rod. The geometric height of the GPS antenna (or of the intersection of the rod with the Earth's surface) is determined for each rod, and the geometric height difference is determined, using standard GPS measurements (accurate to within a few meters). The orthometric height difference for each GPS antenna is determined using the measured GPS location of each rod and an ellipsoid or geoid that approximates the local shape of the Earth's surface.
Method and apparatus for surveying the length, width, height and local slope of a road is disclosed by Gebel in U.S. Pat. No. 5,075,772. A sequence of equally spaced optical markers must be positioned along the road, and these markers are sensed by two video cameras and/or electromagnetic sensors, mounted on a vehicle and directed at the road surface, as the vehicle moves along the road.
A surveying instrument that uses GPS measurements for determining location of a terrestrial site that is not necessarily within a line-of-sight of the surveyor is disclosed in U.S. Pat. No. 5,077,557, issued to Ingensand. The instrument uses a GPS signal antenna, receiver and processor, combined with a conventional electro-optical or ultrasonic range finder and a local magnetic field vector sensor, at the surveyor's location. The range finder is used to determine the distance to a selected mark that is provided with a signal reflector to return a signal issued by the range finder to the range finder. The magnetic field vector sensor is apparently used to help determine the surveyor's location and to determine the angle of inclination from the surveyor's location to the selected mark.
In U.S. Pat. No. 5,146,231, Ghaem et al disclose an electronic direction finder that avoids reliance on sensing of terrestrial magnetic fields. The apparatus uses a directional antenna and receiver/processor for GPS or similar navigation signals received from a GPS satellite, and requires (stored) knowledge of the present location of at least one reference GPS satellite from which signals are received. The orientation of the finder or its housing relative to a line of sight vector from the finder to this reference satellite is determined. This orientation is visually displayed as a projection on a horizontal plane. Any other direction in this horizontal plane can then be determined with reference to this projection from a knowledge of the reference satellite location.
Spradley et al disclose a geodetic survey system using three or more fixed GPS base stations in U.S. Pat. No. 5,155,490. The location of each non-movable base station is known with high accuracy, and each base station has an atomic standard clock and GPS receiver/processor therein to determine GPS satellite clock offset and clock drift for each of several GPS satellites. A mobile station receives GPS signals and receives synchronized radio signals from each of the base stations, in a manner analogous to a LORAN system, and determines the present location and observation time for the mobile station.
With the exception of the Riszkowski and Ingensand approaches discussed above, none of the approaches discussed above is portable and self-contained and allows use in an arbitrary environment. Further, none of these approaches allows definition of baselines for the location determination equipment as the mapping proceeds. What is needed is a portable SATPS survey system that: (1) provides distance and bearing measurements from an observation site to an object to be mapped; (2) is not affected by the presence of a metallic structure that would severely compromise the accuracy of a magnetic compass used at the site; (3) does not require that any part of the survey system be positioned adjacent to or contiguous to the object; (4) can be applied to opaque, semi-opaque or transparent objects; (5) provides location data for an object with inaccuracies of at most a few meters; (6) provides one or more baselines for determination of object locations as the mapping proceeds; and (7) is flexible and can be used in almost any environment where at least a few SATPS satellites are visible.